1) 120 2
2) (1,30)
3)
0<=x<=1/3时,60(0.5-x)-30x<=10
2/9<=x<=1/3
1/3<=x<=0.5时,30x-60(0.5-x)<=10
1/3<=x<=4/9
0.5<=x<=1时,30x-60(x-0.5)<=10
2/3<=x<=1
1<=x<=2时,60(x-0.5)-30x<=10
1<=x<=4/3
x>=2时,90-30x<=10
8/3<=x<=2
综合为:当x位于[2/9,4/9] 、 [2/3,4/3] 及 [8/3,2] 三段时间内二船之间距离小于10KM。